Where are you viewing the dashboard? On the actual tableau server, or through an embed link?

I would recommend that you use the embed link to view the dashboard, it might solve this issue for you - you can access this link by hitting the 'Share' button on the dashboard view, then copying the text under 'Link' into a new browser window.

If tabs are still persisting in this view, look through the link for any indication of an option like showTabs=true that you would be able to toggle.

I'm referring to the actual link from the share button found on my previous image. Once you click share, a dialog box opens with a link to embed and share the dashboard. The second link in the container can be used to open the dashboard on a separate window without the Tableau server interface. Within the link, if tabs are shown the actual URL will include an option such as 'showTabs=true' which can be set the 'showTabs=false' when you distribute the link if you would not like to see tabs.

Hope that makes sense, it will be easy to see once you have the server back up and running.

When you're uploading to the server you're certain that you are checking show tabs as off right? I would suggest overwriting the dashboard by uploading it again to the server and ensuring the option for tabs is ticked off.